1. Field of the Invention
This invention is directed to a pellet stack length recording system, and more particularly to a nuclear fuel pellet stack segment length recording switch for automatically triggering a length measurement by the recording system.
2. Background Information
A nuclear fuel rod contains fissile material in the form of a plurality of generally cylindrical nuclear fuel pellets maintained in a row or stack thereof in the rod. One type of nuclear fuel rod, for example, is a zoned fuel rod which contains short lengths of "blanket" pellets at each end. Other fuel rod designs additionally have fuel pellets stacked in three or more zones of different pellet types including end zones of the blanket pellets. The different types of the fuel pellets include natural, enriched and enriched coated.
Fuel stacks for nuclear fuel rods may be collated by an automatic or a manual system. An example of an automatic system is disclosed in U.S. Pat. No. 4,842,808 issued Jun. 27, 1989 to Stuart L. Rieben et al. entitled "Nuclear Fuel Pellet Collating System" and assigned to the assignee of the present invention, which is herein incorporated by reference.
The manual collating system consists of an operator work area for handling pellets, input pellet trays, and output pellet trays. The manual collating system further consists of linear measuring equipment having a linear scale, a standard commercial weight scale, a barcode reader, and a local data collection computer. The operator work area includes an angled table about which is conveniently mounted the input pellet tray, the output pellet tray, the linear measuring equipment, and the weight scale.
The linear measuring equipment includes a support frame having an X-Y positioning device and a digital scale. The X-Y positioning device supports a measuring arm, a measuring head and a measuring probe. The operator positions the measuring probe in order to obtain measurements from the digital scale. The digital scale records the X coordinate length and transmits the length measurement to the local data collection computer.
The weight scale includes a fixture for supporting the output pellet tray during a weighing operation. The weight scale transmits the weight measurement to the local data collection computer.
The barcode reader is connected to the local dam collection computer and provides an error free identification of the input material (e.g., the pellets). The corrugated metal input pellet trays hold the pellets and include barcode identification labels. Whenever the identification labels are scanned by the barcode reader, the reader transmits the identification of the input material to the local data collection computer in order to verify the type of material prior to use at the operator work area.
The local data collection computer, such as a desk top IBM compatible personal computer, prompts the operator during the collating process, records and verifies the pellet stack segment length and weight measurements which are taken by the operator during the stack building process, and communicates the pellet and fuel rod data to an historical data collection computer.
Accurate pellet stack segment length measurements are essential for proper quality control and nuclear fuel rod operation. In the manual system, the length measurements are provided by the linear measuring equipment which includes the manually positioned measuring probe and the digital scale. Pellet stacks typically are assembled for a lot of 25 fuel rods at a time. The pellets for each lot are contained in special trays in a container or cassette. Due to the length of the cassette trays, each stack may consist of 9 or more segments. A typical 25 fuel rod lot, or one cassette, having 11 segments, requires 11 measurements to be recorded per rod, or 275 individual length measurements per cassette.
Pellets are separated on an input tray for the zone, or a segment of the zone, row by row for each of 25 rows on the tray. Each row represents a segment of a fuel stack. The pellets, separated for the zone or segment, are measured and recorded row by row, starting with the front row and moving to the rear row. The accuracy of the pellet stack segment linear measuring equipment is provided by a spring preload device which compresses the pellet stack segment, in order to eliminate gaps between pellets, and by a zero length check of the digital scale before and after a group of measurements. Whenever measurements are taken, the operator positions the measuring probe against an individual pellet stack segment, which compresses the spring preload device. Then, the operator actuates a foot switch, in order to signal the digital scale to transmit the length of the pellet stack segment to the local data collection computer.
Although the system provides the capability for accurate length measurements, there is room for improvement. During manual operation, the operator may become overly familiar with the function of the manual system and quickly move through a relatively large number of pellet stack segment length measurements. In particular, the operator's hand - foot coordination may become non-synchronized and, hence, the spring preload device may not be fully compressed before the foot switch is depressed. Accordingly, measurement errors may result. Although these errors are detected by subsequent quality control inspections, rework, such as remeasurement of the pellet stack segments, is required.
There is a need, therefore, for a manual pellet stack segment measurement system that operates independently of the hand - foot coordination of an operator.
There is a more particular need for such a manual measurement system that consistently provides accurate pellet stack segment length measurements.